Internet Bug Bounty · Report #1400238
Path Traversal and Remote Code Execution in Apache HTTP Server 2.4.49 and 2.4.50 (incomplete fix of CVE-2021-41773) (CVE-2021-42013)
Summary
It was found that the fix for CVE-2021-41773 in Apache HTTP Server 2.4.50 was insufficient. An attacker could use a path traversal attack to map URLs to files outside the directories configured by Alias-like directives.
If files outside of these directories are not protected by the usual default configuration "require all denied", these requests can succeed. If CGI scripts are also enabled for these aliased pathes, this could allow for remote code execution.
This issue only affects Apache 2.4.49 and Apache 2.4.50 and not earlier versions.
Acknowledgements:
Reported by Juan Escobar from Dreamlab Technologies Reported by Fernando Muñoz from NULL Life CTF Team Reported by Shungo Kumasaka Reported by Nattapon Jongcharoen
Reported to security team: 2021-10-06 fixed by r1893977, r1893980, r1893982 in 2.4.x: 2021-10-07 Update 2.4.51 released: 2021-10-07 Affects: 2.4.50, 2.4.49
How it was found
It was found that the fix for CVE-2021-41773 in Apache HTTP Server 2.4.50 was insufficient. An attacker could use a path traversal attack to map URLs to files outside the directories configured by Alias-like directives.
This issue only affects Apache 2.4.49 and Apache 2.4.50 and not earlier versions.
My friend Juan Escobar @itsecurityco and me (Fernando Munoz) reported this internally to Apache HTTPd project and worked with them to test the new patch before the new version was released.
Impact
If files outside of these directories are not protected by the usual default configuration "require all denied", these requests can succeed. If CGI scripts are also enabled for these aliased pathes, this could allow for remote code execution.